The effect of midazolam co-induction on cardiorespiratory variables, myoclonus and etomidate dose requirements in healthy cats.

Objective: To evaluate dose requirements of etomidate for endotracheal intubation, with or without midazolam co-induction, and to describe induction quality and associated cardiorespiratory variables in healthy cats.

Study Design: Randomized prospective experimental study.

Animals: A group of 24 adult neutered cats (17 females, seven males).

Methods: Cats were premedicated with intramuscular butorphanol (0.4 mg kg) and alfaxalone (2 mg kg), and anesthesia was induced with etomidate following midazolam (0.3 mg kg) or physiologic saline (0.06 mL kg) intravenously. Heart rate, respiratory rate (f) and arterial blood pressure were measured following premedication, at co-induction, after etomidate administration, and after orotracheal intubation and compared using repeated-measures anova. Pre- and post-etomidate blood samples were assessed for the presence of hemolysis. Etomidate dose requirements and prevalence of myoclonus were compared with Wilcoxon signed ranks test and Fisher's test. Values of p < 0.05 were considered significant.

Results: Mean ± standard deviation etomidate doses required for orotracheal intubation were 0.84 ± 0.26 and 1.39 ± 0.33 mg kg for midazolam and saline co-induction, respectively (p = 0.001). The presence of myoclonus at sedated baseline, co-induction and etomidate was 6/12, 8/12 and 9/12 in the saline group, respectively, and 10/12, 2/12 and 0/12 in the midazolam group. The prevalence of myoclonus was lower in the midazolam group after co-induction and etomidate injection (p = 0.036 and p < 0.001, respectively). Cardiorespiratory variables did not differ between groups at any time point. Compared with baseline, f decreased in both groups after etomidate injection and intubation. Hemolysis was observed in all post-etomidate plasma samples.

Conclusions And Clinical Relevance: Etomidate, with or without midazolam co-induction, provides acceptable cardiovascular function in premedicated healthy cats. Midazolam reduces etomidate requirements for orotracheal intubation and improves induction quality in cats premedicated with intramuscular butorphanol-alfaxalone.